This invention relates in general to plasma display panels and, in particular, to an AC control system for selectively energizing the discharge cells of such a panel.
Plasma display panels currently find widespread use in a number of different applications. An example of this type of display panel is shown and described in the U.S. Pat. to Coleman et al., No. 3,614,769, which is incorporated herein by reference.
This type of display panel is normally comprised of an outer enclosure which is formed by a front and a rear glass plate. The front and rear glass plates of the panel are maintained in a spaced apart relationship and are sealed together along their outer perimeter to provide a hollow inner chamber which is filled with an ionizable medium such as any one of, or a mixture of, the gases neon, argon, helium, kypton, xenon, hydrogen and nitrogen. Matrix addressability is incorporated into the panel by disposing a plurality of vertical electrodes (hereinafter referred to as "column electrodes") on one glass plate of the panel and a plurality of horizontal electrodes (hereinafter referred to as "segment electrodes") on the other glass plate of the panel. The column electrodes are disposed on the inner surface of one plate of the panel to form a parallel array which extends across the plate in a vertical direction. The segment electrodes, on the other hand, are disposed on the inner surface of the other plate of the panel to form a parallel array which extends across the plate in a horizontal direction. In this way, the column and segment electrodes are maintained in a generally orthogonal relationship wherein each column electrode crosses over each segment electrode and vice versa. The point where a column electrode crosses over a segment electrode is referred to as a "cell". In such a display panel, an insulating layer is also placed over the segment and column electrodes to electrically insulate them from the gas contained within the panel, thereby providing capacitive coupling between the electrodes and the gas.
A cell of the matrix is illuminated by applying a suitable electric potential between the segment and column electrodes which form the cell. The application of a suitable electric potential between these two electrodes of a cell causes a gas discharge to occur within the cell. This discharge produces sufficient illumination for use as a visual display. Through the selective application of a suitable electric potential to the column and segment electrodes of the panel, selected groups of cells can be illuminated to provide a visual display of letters, numbers and other characters.
Several different types of control systems for driving such a display panel are presently known. All of these control systems, however, basically fall into one of three categories. Control systems in the first category normally include a pair of driver circuits which cooperate to apply one half of the required voltage to the segment electrode associated with the cell to be illuminated and the other half of the voltage to the column electrode associated with the cell. The resultant voltage is sufficient to initiate a discharge within the discharge cell which is disposed between these two electrodes.
Control systems of the second type normally include a driver circuit for each segment and column electrode and a switching circuit for each segment and column electrode. The driver and switching circuits cooperate to illuminate a designated cell by alternately energizing the column and segment electrodes associated with the cell while the cell's other electrode is electrically coupled with ground. In this way, the voltage needed to initiate a discharge is initially applied, for example, to the column electrode associated with a designated cell while the segment electrode associated with the cell is grounded. Thereafter, the required voltage is applied to the segment electrode associated with the designated cell while the cell's column electrode is grounded. The drive scheme continues in this fashion until the cell is no longer designated for illumination.
The final category of control system typically includes driver circuitry for selectively providing a bipolar pulse wave to either the column or segment electrodes and switching circuitry for selectively coupling the other electrodes to ground. In this configuration, a discharge occurs within a designated cell whenever one of the electrodes associated with the cell is receiving the pulse wave while the other electrode associated with the cell is electrically coupled with ground. In particular, a discharge occurs each time the positive or negative component of the pulse wave obtains a voltage sufficient to cause a discharge to occur.
While these prior art control systems exhibit adequate operation, none of them has proved to be totally satisfactory from a manufacturing standpoint. In particular, all of the presently-available control systems require the use of transistors which are capable of handling high voltages and, as a result, cannot be formed by monolithic integrated circuits. Accordingly, the prior art control systems are difficult and expensive to manufacture. Another disadvantage associated with the control systems of the prior art is that they tend to be complex in design and operation.